Implement BrowserAccessibility accNavigate() in terms of AXPlatformNodeWin.

Here we are implementing one more IAccessibility method, accNavigate(), in
terms of ui::AXPlatformNodeWin. The idea is that we can forward
IAccessibility calls to ui::AXPlatformNodeWin and then slowly trim down,
and maybe remove, BrowserAccessibilityWin.

Note that this does not forward NAVDIR_. That will be a follow up.

BUG=703369

patch from issue 2789333002 at patchset 40001 (http://crrev.com/2789333002#ps40001)

Review-Url: https://codereview.chromium.org/2806963002
Cr-Commit-Position: refs/heads/master@{#463273}
2 files changed